The present invention disclosed herein relates to a light emitting device using an alternating current (AC) light emitting diode (LED), and more particularly, to a light emitting device using an AC LED which turns on at least one AC LED array in an AC LED light emitting unit including at least two AC LED arrays each of which includes at least one AC LED within one period of an AC power (e.g., AC 110V, AC 220V, or the like).
Generally, for an AC LED light emitting device adopting an AC LED light emitting unit, which includes at least two AC LED arrays each of which includes at least one AC LED, as a light source, a voltage of an AC power such as an AC 110V or AC 220V is decreased to a driving voltage and supplied to the AC LED light emitting unit.
FIG. 1 is a diagram illustrating a conventional AC LED light emitting device.
The conventional AC LED light emitting device illustrated in FIG. 1 decreases a voltage of an AC power (e.g., AC 110V, AC 220V, or the like) to a driving voltage using a resistor and supplies the driving voltage to an AC LED light emitting unit.
Referring to FIG. 1, the conventional AC LED light emitting device 100 includes an AC power unit 110, an AC LED light emitting unit 120, and a voltage dropping unit 130.
The AC power unit 110 provides the AC power such as the AC 110V or AC 220V through power output terminals L1 and L2.
The AC LED light emitting unit 120 includes a first AC LED light emitting unit 121 and a second AC LED light emitting unit 122. The first AC LED light emitting unit 121 includes at least two AC LED arrays connected to each other in series, where each AC LED array includes at least one AC LED connected in a forward direction to the terminal L1 of the AC power unit 110. The first AC LED light emitting unit 121 is turned on when a phase of a voltage V1 of the AC power is positive. The second AC LED light emitting unit 122 includes at least two AC LED arrays connected to each other in series, where each AC LED array includes at least one AC LED connected in a forward direction to the terminal L2 of the AC power unit 110. The second AC LED light emitting unit 122 is connected in parallel to the first AC LED light emitting unit 121. The second AC LED light emitting unit 122 is turned on when the phase of the voltage V1 of the AC power is negative.
For reference, it is exemplarily illustrated in FIG. 1 that the first AC LED light emitting unit 121 includes 4 AC LED arrays LED1, LED3, LED5, and LED7 connected to each other in series, where each AC LED array includes at least one AC LED connected in a forward direction to the terminal L1 of the AC power unit 110. Also, it is exemplarily illustrated that the second AC LED light emitting unit 122 includes 4 AC LED arrays LED2, LED4, LED6, and LED 8 connected to each other in series, where each AC LED array includes at least one AC LED connected in a forward direction to the terminal L2 of the AC power unit 110, being connected in parallel to the first AC LED light emitting unit 121.
The voltage dropping unit 130 includes a first resistor R1 installed between the terminal L1 of the AC power unit 110 and the AC LED light emitting unit 120 for dropping a voltage and a second resistor R2 installed between the terminal L2 of the AC power unit 110 and the AC LED light emitting unit 120 for dropping a voltage. The voltage dropping unit 130 drops the voltage V1 of the AC power to the driving voltage and supplies the driving voltage to the AC LED light emitting unit 120.
The first resistor R1 drops the voltage V1 of the AC power to the driving voltage and supplies the driving voltage to the first AC LED light emitting unit 121 when the phase of the voltage V1 of the AC power is positive.
The second resistor R2 drops the voltage V1 of the AC power to the driving voltage and supplies the driving voltage to the second AC LED light emitting unit 122 when the phase of the voltage V1 of the AC power is negative.
The voltage dropping unit 130 may further include a Positive Temperature Coefficient Resistor (PTCR) between the AC power unit 110 and the AC LED light emitting unit 120. The PTCR is capable of controlling a current applied to the AC LED light emitting unit 120 according to a change of temperature of the AC LED light emitting unit 120.
It is preferable to connect the PTCR in parallel to the first resistor R1 as illustrated in FIG. 1. The PTCR decreases the current applied to the AC LED light emitting unit 120 if the temperature increases due to turn-on of the AC LED light emitting unit 120.
An operation of the AC LED light emitting device 100 is described as follows.
When the phase of the voltage V1 of the AC power such as AC 110V or AC 220V provided by the AC power unit 110 is positive, the 4 AC LED arrays LED1, LED3, LED5, and LED7 of the first AC LED light emitting unit 121 including at least one AC LED connected to each other in series and connected in a forward direction to the terminal L1 of the AC power unit 110 are turned on by the driving voltage supplied through the first resistor R1. At this time, the second AC LED light emitting unit 122 connected in parallel to the first AC LED light emitting unit 121 in a reverse direction is not turned on.
On the contrary, when the phase of the voltage V1 of the AC power is negative, the 4 AC LED arrays LED2, LED4, LED6, and LED8 of the second AC LED light emitting unit 122 including at least one AC LED connected to each other in series and connected in a forward direction to the terminal L2 of the AC power unit 110 are turned on by the driving voltage supplied through the second resistor R2. At this time, the first AC LED light emitting unit 121 connected in parallel to the second AC LED light emitting unit 122 in a reverse direction is not turned on.
FIG. 2 is a diagram illustrating another conventional AC LED light emitting device. A size of the AC LED light emitting unit 120 including two AC LED light emitting units 121 and 122 illustrated in FIG. 1 is reduced to a half. That is, two AC LED light emitting units are reduced to one, and one AC LED light emitting unit is connected in a forward direction to the AC power regardless of polarity of the AC power by using a diode bridge.
The conventional AC LED light emitting device of FIG. 2 drops the voltage of the AC power to the driving voltage of the AC LED light emitting unit using the resistor, and then, full-wave rectifies the driving voltage through the diode bridge which connects the AC LED light emitting unit in a forward direction to the AC power regardless of the polarity of the AC power to supply the rectified driving voltage to the AC LED light emitting unit.
Referring to FIG. 2, the conventional AC LED light emitting device 200 includes an AC power unit 210, an AC LED light emitting unit 220, a voltage dropping unit 230, and a diode bridge 240.
The AC power unit 210 provides the AC power such as the AC 110V or AC 220V through power output terminals L1 and L2.
The AC LED light emitting unit 220 includes at least two AC LED arrays connected to each other in series, where each AC LED array includes at least one AC LED connected in a forward direction to the AC power. The AC LED light emitting unit 220 is turned on when the phase of the voltage V1 of the AC power is positive or negative.
For reference, it is exemplarily illustrated in FIG. 2 that the AC LED light emitting unit 220 includes 4 AC LED arrays LED1 to LED4 connected to each other in series, where each AC LED array includes at least one AC LED connected in a forward direction to the AC power.
The voltage dropping unit 230 includes a first resistor R1 installed between the terminal L1 of the AC power unit 210 and the AC LED light emitting unit 220 for dropping a voltage and a second resistor R2 installed between the terminal L2 of the AC power unit 210 and the AC LED light emitting unit 220 for dropping a voltage. The voltage dropping unit 230 drops the voltage V1 of the AC power to the driving voltage and supplies the driving voltage to the AC LED light emitting unit 220.
The first resistor R1 drops the voltage V1 of the AC power to the driving voltage and supplies the driving voltage to the AC LED light emitting unit 220 when the phase of the voltage V1 of the AC power is positive.
The second resistor R2 drops the voltage V1 of the AC power to the driving voltage and supplies the driving voltage to the AC LED light emitting unit 220 when the phase of the voltage V1 of the AC power is negative.
The voltage dropping unit 230 may further include a PTCR between the AC power unit 210 and the AC LED light emitting unit 220. The PTCR is capable of controlling a current applied to the AC LED light emitting unit 220 according to a change of temperature of the AC LED light emitting unit 220.
It is preferable to connect the PTCR in parallel to the first resistor R1 as illustrated in FIG. 2. The PTCR decreases the current applied to the AC LED light emitting unit 220 if the temperature increases due to turn-on of the AC LED light emitting unit 220.
The diode bridge 240 is a full-wave rectifying circuit where four diodes are connected in a rhombus shape forming a positive connection node N1, a negative connection node N2 facing the positive connection node N2, and a pair of input/output nodes N3 and N4 facing each other between the positive connection node N1 and the negative connection node N2. The diode bridge 240 connects the AC LED light emitting unit 220 in a forward direction to the AC power regardless of the polarity of the AC power and full-wave rectifies the driving voltage supplied through the voltage dropping unit 230 to supply the rectified driving voltage to the AC LED light emitting unit 220.
The first resistor R1 of the voltage dropping unit 230 is connected to the positive connection node N1 of the diode bridge 240, and the second resistor R2 of the voltage dropping unit 230 is connected to the negative connection node N2. The AC LED light emitting unit 220 is connected in a forward direction to the AC power unit 210 between the pair of the input/output nodes N3 and N4.
The diode bridge 240 full-wave rectifies the driving voltage supplied through the first resistor R1 of the voltage dropping unit 230 and supplies the rectified driving voltage to the AC LED light emitting unit 220 when the phase of the voltage V1 of the AC power is positive.
The diode bridge 240 full-wave rectifies the driving voltage supplied through the second resistor R2 of the voltage dropping unit 230 and supplies the rectified driving voltage to the AC LED light emitting unit 220 when the phase of the voltage V1 of the AC power is negative.
An operation of the conventional AC LED light emitting device 200 is described as follows.
When the phase of the voltage V1 of the AC power such as AC 110V or AC 220V provided by the AC power unit 210 is positive, the 4 AC LED arrays LED1 to LED4 of the AC LED light emitting unit 220 including at least one AC LED connected to each other in series and connected in a forward direction to the terminal L1 of the AC power unit 210 are turned on by the driving voltage supplied after being full-wave rectified through the first resistor R1 and the diode bridge 240. At this time, the current flows through the positive connection node N1, the input/output node N3, the 4 AC LED arrays LED1 to LED4 of the AC LED light emitting unit 220, the input/output node N4, and the negative connection node N2 shown in FIG. 2.
On the contrary, when the phase of the voltage V1 of the AC power is negative, the 4 AC LED arrays LED1 to LED4 of the AC LED light emitting unit 220 including at least one AC LED connected to each other in series and connected in a forward direction to the terminal L1 of the AC power unit 210 are turned on by the driving voltage supplied after being full-wave rectified through the second resistor R2 and the diode bridge 240. At this time, the current flows through the negative connection node N2, the input/output node N3, the 4 AC LED arrays LED1 to LED4 of the AC LED light emitting unit 220, the input/output node N4, and the positive connection node N1.
Meanwhile, the AC power such as the AC 110V or AC 220V supplied to the above-described conventional AC LED light emitting devices 100 and 200 shows since wave characteristics having a positive polarity at a phase of 0° to 180° and a negative polarity at a phase of 180° to 360° within one period with a frequency of generally 60 Hz as illustrated in FIG. 3A.
Also, according to the conventional AC LED light emitting devices 100 and 200, as the number of the AC LED arrays included in the AC LED light emitting units 120 and 220 connected in a forward direction to the AC power such as the AC 110V or AC 220V is increased, a turn-on voltage, i.e., a forward threshold voltage, is increased. Only when magnitude of the voltage applied to the AC LED light emitting units 120 and 220 is larger than the turn-on voltage, the current flows to the AC LED light emitting units 120 and 220 so that they are turned on. Herein, the current applied to the AC LED light emitting units 120 and 220 flows to the AC LED light emitting units 120 and 220 only when the magnitude of the voltage is larger than the turn-on voltage at the phase of 0° to 180° where the phase of the voltage V1 of the AC power is positive as illustrated in FIG. 3B. Also, the current flows to the AC LED light emitting units 120 and 220 only when the magnitude of the voltage is larger than the turn-on voltage at the phase of 180° to 360° where the phase of the voltage V1 of the AC power is negative.
Actually, at the phase of 0° to 180° where the phase of the voltage V1 of the AC power showing the sine wave characteristics is positive, if it is assumed that a time taken for the magnitude of the voltage to reach the turn-on voltage is t1, a time where the magnitude of the voltage is kept as higher than the turn-on voltage is t2, and a time where the magnitude of the voltage drops below the turn-on voltage again is t3, the current applied to the AC LED light emitting units 120 and 220 flows to the AC LED light emitting units 120 and 220 only during the time t2. Herein, the time t1 corresponds to a phase of approximately 0° to 45° where the phase of the voltage V1 of the AC power is positive, the time t2 corresponds to a phase of approximately 45° to 135° where the phase of the voltage V1 of the AC power is positive, and the time t3 corresponds to a phase of approximately 135° to 180° where the phase of the voltage V1 of the AC power is positive.
Also, at the phase of 180° to 360° where the phase of the voltage V1 of the AC power is negative, if it is assumed that that a time taken for the magnitude of the voltage to reach the turn-on voltage is t4, a time where the magnitude of the voltage is kept as higher than the turn-on voltage is t5, and a time where the magnitude of the voltage drops below the turn-on voltage again is t6, the current applied to the AC LED light emitting units 120 and 220 flows to the AC LED light emitting units 120 and 220 only during the time t5. Herein, the time t4 corresponds to a phase of approximately 180° to 225° where the phase of the voltage V1 of the AC power is negative, the time t5 corresponds to a phase of approximately 225° to 315° where the phase of the voltage V1 of the AC power is negative, and the time t6 corresponds to a phase of approximately 315° to 360° where the phase of the voltage V1 of the AC power is negative.
However, according to the conventional AC LED light emitting devices 100 and 200, as illustrated in FIG. 3B, in one period of the phase of the voltage of the AC power having the sinusoidal characteristics, if the current is applied to the AC LED light emitting units 120 and 220 only during the time t2 corresponding to the phase of approximately 45° to 135° where the phase of the voltage V1 of the AC power is positive and the time t5 corresponding to the phase of approximately 225° to 315° where the phase of the voltage V1 of the AC power is negative, lighting efficiency of the AC LED light emitting units 120 and 220 is degraded and power consumption is increased. Further, due to discontinuity of the operating current, a Total Harmonic Distortion (THD) is high having approximately 40% to 50%, and a flicker occurs excessively.